Fuse plug



c. E. o. KRlEGSTEDT FUSE PLUG Filed Jan. 12, 1932 ,Patented Sept. 19, 1933 UNITED STATES FUSE PLUG Carl E. 0. Kriegsfedt,

Washington, D. 0., as

signor to the Engineering Appliance Corporation, a corporation of Application January 12,

Delaware 1932. Serial No. 586,120

6 Claims. (Cl. 200-121) This invention relates to fuses such as are used in connection with electrical wiring systems and has special reference to a blow out indicating fuse plug. i

'As is well known, it is frequently quite diflicult to determine by visual inspection which of several fuse plugs has blown out when a blow out occurs in a wiring system because most fusesof the plug type'depend upon the discoloration of a mica plate to indicate the blow out and such fuses are generally in a place which is inadequately lighted for such observance.

One important object of' the present invention is to provide an improved general construction of electric fuse wherein the blowing out 'of the fuse member will cause a luminous element within the fuse assembly to glow.

A second important object of the invention is to provide a novel general construction of fuse plug embodying a self-contained luminous element in shunt with the fusible member of the plug that will glow only after the fusible element has been ruptured and will continue to glow until 9. new fusible element has been substituted for the blown or ruptured fusible element, even after the short circuit has been removed from the electrical wiring system, which short circuit originally caused the fusible element to become ruptured.

A third object of the invention is to provide a luminous indicating meansof such'small current consumption that it will glow when used on alternating current circuits, having as low an electrical capacity as .301 mi. Y

A fourth object of the present invention is to provide a luminous indicating means of such small current consumption that when used as a protective means on delicate instrument circuits, will not pass sufflcient current to injure the instrument.

ith the above and other objects in view as will be hereinafter apparent, the invention consists in general of certain novel details of con-=- struction' and combinations of parts hereinafter fully described, illustrated in the accompanying drawing and specifically claimed. I

In the accompanying drawing like characters of reference indicate like parts in the several views, and:

figure l is a section through the improved device taken diametrically through the longitudinal axis of the plug.

.Figure 2 is a bottom view of the middle or lamp carrying member of the plug,

part 11 of this shell is smoothly cylindrical and 66.

between this lower part and the threaded portion there isan internal flange 12.

Within the shell is mounted a block of insulating material having. a peripheral rib 13 which rests on the flange 12. Below the flange the block is provided with an inverted frusto-conical lower end 14 and extending downwardly into the block from its upper face is an inverted frustoconical recess 15.) Also the block is provided at its lower end with a shallow recess 18 from whence extends a radial channel 17. Extending. upwardly from the recess 16 into the recess 15 is a lamp terminal 18 provided with a suitable fiat head in the recess 16.- This lamp terminal supports a miniature lamp 119 the other terminal 20 of which is connected to one end of a resistance strip 21. The remaining end of this strip 21 is connected to the shell by a conductor 22.

Removably seated within the lower portion 11 of the shell is a cylindrical cup 23 of insulating material which covers the lower portion of the middle insulating member. A contact button or plug 24 extends centrally through the bottom of the cup 23 so that it may.seat on the central contact of a standard plug socket. The fusible g0 strip consists of a ribbon like body 25 of proper cross section to fuse or blow out upon the amperage desired being exceeded. At one end of this body is a circular head 26. Inuse the head 26 is placed in thelrecess 16 to bearagainst the terminal is and the body 25 is led through the channel 17 over the edge of the cup, being held by the cup in contact with the shell and by the button 24 in contact with the lamp terminal. A transparent glass can 27 is screwed into the upper part of the shell holds the middle insulator in positi u and protects the lampl ill.

As sheen in Figure 4% the device is connected in series between a line 28 and a circuit Wire 29, the farmer being shown connected to the button 24 and the latter to the shell 10. Now the resistance 21 is so arranged that it offers so much resistance to the current that under normal conditions substantially all the current will flow through the fusible member so that the lamp will not glow. However, if the fusible element blows out then .thecurrent, resisted by resistance 21,

.will flow through the lamp sufilciently to cause glowing thereof. 'By this means the blowing out of a fuse can be readily detected. The miniature lamp 19 consists of a small sealed glass tube charge with a gas under pressure and provided with suitable electrodes, the gas being of such a character that it produces a luminous glow when electric circuit is passed therethrough, the pressure of the gas and the spacing of the electrodes being determined by the voltage to be impressed on the electrodes, and having a current limiting resistance 21 in series with one of the electrodes. The lamp employed is so designed that it will glow with a current of four micro-amperes and this amount being amply provided by an alternating current circuit having a capacity of .301 mf. From this it will be quite obvious that the luminous means 19 will draw its energy through a capacity effect and not through any leakage that may occur in the circuit and will operate on circuits having the highest insulation resistance and in addition, will glow after the short circuit has been removed and the circuit'open.

By referring to Figure 1 of the drawing, it will be noted that the fusible element 25 is arranged The glass cap may be held against accidental unscrewing by a drop of solder placed on the edge of the shell and entering a slot 30 in the cap.

There has thus been provided a simple and ciiicient device of the kind described and for the purpose specified.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, therefore, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

Having thus described the invention, what is claimed as new, is:

1. A fuse plug including a metallic shell adapted to engage in a standard socket, an insulating body in said shell, a pilot lamp supported by said body, a resistance element connected in series between one terminal of said pilot lamp and shell, a fusible member connecting the other terminal of the lamp and the shell, a cup closing the lower end of the shell and having a contact button arranged to conduct current to the last mentionedterminal from a standard socket, and a glass cap closing, the upper end of the shell and covering the lamp.

2. A fuse plug including a metallic shell adapted to engage in a standard socket, an insulating body in said shell having a recess in its lower end, a lamp above said body having one of its terminals entering said recess, a cup closing the lower end of said shell, 2. contact button extending through the bottom of said cup, a fusible strip having one end clamped between said button and said terminal and having its other end clamped between said cup and shell, and a resistance element connected in series between the remaining terminal of said lamp and the shell.

3. A fuse plug including a metallic shell adapted to engage in a standard socket, an insulating body in said shell having a recess in its lower end, a lamp above said body having one its terminals entering said recess; a cup closing the lower end of said shell, a contact button extending through the bottom of said cup, a fusible strip having one end clamped between said button and said terminal and having its other end clamped between said cup and shell, a resistance element connectedin series between the remaining terminal of said lamp and the shell, and a glass cap closing the upper end of the shell and covering the lamp.

4. A plug fuse unit comprising a casing formed of insulating material and having an open end recess therein, a luminous indicating means cohsisting of an electro-luminous gas filled bulb arranged within said recess, a current limiting resistance arranged within said recess, and in series with the electrodes of said bulb, a contact terminal arranged about said casing, is fusible element, a holder for said fusible element, a contact terminal carried by said holder, said holder having .detachable connection with said casing for retaining said fusible element in contact with said terminals and at a point upon said casing opposite to the recess formed therein in order to separate the fusible element from said luminous indicating means, independent means for connecting said, luminous indicating means and resistance to said terminals, and said luminous indicating means being capable of operating on a low current capacity that when said fusible element is blown said luminous indicating means will glow on an open circuit having a low electrical capacity.

5. A fuse unit comprising a casing having two separate compartments, one of said compartments having an opened end, a transparent cap secured to said casing and closing the compartment thereof having an opened end, a glow lamp arranged within said compartment which is covered by said transparent cap, ,a fusible element arranged within the other of said compartments, contact terminals arranged about said casing and said fusible element and glow lamp being electrically connected to said contact terminals whereby shell, a transparent cap secured to said shell and covering the opened end thereof in which is arranged said pilot lamp, a holder detachably connected to said shell for covering the opposite opened end thereof, a contact terminal carried by said holder, a fusible element supported by said holder, said fusible element being electrically connected to said contact terminals when said holder is attached to said shell, and independent 'means connecting said pilotlamp with said con- 

